Heat exchange structure



Feb- 1, 1966 F. A. LOEBEL ETAL 3,232,280

HEAT EXCHANGE STRUCTURE Filed Jan. 30, 1964 INVENTORS FQEDEQICK A. LOEBEL GROBECKER ,W 1 #WZ- HUGO H. BY dm/,J

United States Patent C) 3,232,280 HEAT EXCHANGE STRUCTURE Frederick A. Loebel and Hugo H. Grohecker, both of Milwaukee, Wis., assignors to Cleaver-Brooks Company, a corporation of Wisconsin Filed Ian. 30, 1964, Ser. No. 341,268 7 Claims. (Cl. 122-149) This invention relates to heat exchange apparatus, especially to such apparatus for use in boilers and the like. Particularly, the present invention lrelates to heat exchange tubes and also to assemblies in boilers including the same.

In heat exchange apparatus using heat exchange tubes wherein fluids are passed through the tubes in heat exchange with an adjacent chamber, the iiuid passed through the tubes may leave deposits which will eventually collect to an extent Where the tubes -becorne clogged, either completely plugged or at least sufficiently restricted to be rendered greatly less efficient for their intended purpose. For example, where combustion gases are passed through heat exchange tubes in heat exchange with a body of Water in a boiler assembly for heating the water, non-burnable or unburned materials in the combustion gases tend to deposit Withinthe tubes before the combustion gases are exhausted from the system. Thus, it is necessary to periodically clean such heat exchange tubes.

In the cleaning of heat exchange tubes, soft deposits yare normally removed by brushes which are pushed through the length of each tube, often with rotary movement applied to the brush.

It has been proposed to provide internal projections on the interior surfaces of heat exchange tube-s for the purpose of improving the heat exchange efficiency of the tube 'by providing greater heat exchange surface area and/or by causing turbulent -ow therethrough for more intimate contact of all of the combustion gases with the tube Wall. However, such internal projections may often obstruct brush passage vand/or brush rotation during cleaning operations. At least, the projections normally tend to cause undue bristle bending in a brush pushed through the tube, thereby decreasing the effectiveness of the brush in the cleaning operation. The projections can also protect the deposits from the action of the brush.

It is a general object of this invention to provide new and useful heat exchange tubes having readily cleanable internal surfaces.

It is also an object of this invention to define a spiral path for direction of a cleaning brush along the interior surface -of a heat exchange tube.

It is further an object of this linvention to provide a heat exchange tube having internal projections arranged for improved cleaning of the tube interior While still retaining any advantage of the projections relative to eficiency, turbulent flow, etc.

Still another object is to provide heat exchange tube assemblies and boiler structures including heat exchange tubes of the above objects.

Other objects of this invention will be apparent from the following descriptions and the drawings in which:

FIGURE 1 is a vertical section through a boiler incorporating an embodiment of -heat exchange apparatus in accordance herewith;

FIGURE 2 is a perspective View of a portion of the length of a heat exchange tube, enlarged from FIGURE l, and illustrating a form of the present invention; and

FIGURE 3 is a section through a heat exchange tube such as shown in FIGURE 2 more precisely illustrating an exemplary form of the heat exchange tube.

. While this invention is susceptible of embodiment in many different forms, there is Ishown in the drawings and 3,232,280- Paterr'ted Feb. l, 1966 ice will herein be described in detail, a specific embodiment of the invention with the Iunderstanding that the present disclosure is to be considered as an exemplification of the principles of the Vinvention and is not intended to limit the invention to the embodiment illustrated.

Turning first briefly to FIGURE 1, there is illustrated a 'boiler structure including heat exchange tubes 10 supported between a pair vof opposing tube sheets. The boiler structure and the general operation of the boiler will beV discussed in more detail hereinbelow.

Still considering FIGURE l and turning especially to FIGURES 2 and 3, heat exchange tubes 1t) will rst be considered in more detail. Each tube 19 comprises a iistulous member provided with means for directing a cleaning brush in a spiral path along the tube interior. The means are illustrated as a series of internal projections in the form of clomelike spaced b-osses 11 which may readily be create-d by indentation of the exterior of the tube wall resulting in formation of the corresponding boss 11 on the interior Wall, the wall being actually deviated inward to define the boss. The bosses can, of course, be formed in other ways, eg. as solid bosses secured to the tube inner wall. Bosses 11 are disposed in spiral `array along the length of each tube 10 on the interior surface thereof. Each tube 1G has two opposing open ends, ea-ch open end being capable of support through and by a tube sheet in normal boiler assembly fashion.

The bosses 11 on the interior of tube 10 permit greater efficiency in heat exchange as described by Cleaver et al. in application Serial No. 291,674, entitled Heat Exchange Apparatus, tiled July l, 1963. This case and said application have a common assignee.

The spiral disposition of the internal or interior projections of the heat exchange tube wall improves the cleanability of the tube interior. In cleaning the tube, the boiler permits accessibility to bot-h tube ends and a long brush is pushed through the tube. The spiral disposition of the projections 11 promotes rotary movement of the Ibrush and may actually direct the brush in a spiral path. Thus, the brush is more easily rotatable as it is passed down the tube for more effective cleaning. Further, it has been found when cleaning such tubes that the spiral arrangement of the internal projections tends to pull the brush through the length of the tube, especially when rotary motion is imparted to the brush.

In the preferred use, the tubes 10 are disposed within the boiler on an incline as shown in FIGURE l. In this form, there is provided an unknobbed or boss-free generally linear surface 12 for permitting gravity drainage of condensed liquids from the tubes, e.g. upon cessation of flow of combustion gases therethrough. In this form, the lower surface 12 of each mounted tube is essentially a longitudinal portion of the tubular inner surface and may be considered as a drainage trough in the bottom of the tube interior, free from internal obstruction by the bosses 11.

As best seen in FIGURE 3, and as a specific example of ka suitable heat exchange tube, a heat exchange tube having lan outer diameter of about 21/2 and an inner diameter of about 2%" has been d-inrpled by pressing indentations or dimples inward toward the center of the tube .from the outside surface thereof lto form interior bosses. The bosse-s are in helical array and each helical convolution includes fou-r bosses disposed `an angular distance of from each other, center-to-center. The bosses of one such convolution are identified `as 11a through 11d .in FIGURE 3. Each dimiple in cross-section lat the center thereof has a radius R1 of 9/16. The internal radius R2 of the bend joining each boss with the contiguous laterally adjacent tube wall is about bym. Thev bosses in each convolution are staggered and oset approximately 1". The dimples are each about W16 deep. The first dimple of one helical convolution is disposed about 4 from the first dimple of the next adjacent convolution.

Other means on the interior surface may be used in lieu of the spiral array of bosses for directing the cleaning Ibrush in a spiral path through the tube. For example, elongate ribs 'or fins o-f spiral configuration may be secured over 'a portion of the tube length or may extend the entire tube length. One or more of said fins, preferably parallel, may be used. Other brush directing congurations, e.g. corrug-ations and the like, will be apparent to those in the art :from the examples given herein.

Turning now to FIGURE 1 yand considering the boiler assembly in which the heat exchange tubes are disposed, the boiler includes a casing composed of a metal shell 13, a refractory end cap 14 and an end plate 15. The boiler casing is supported by legs 18 from pedestal 19. Within the boiler, heat exchange passages for flow of combustion gases and water are provided. The fiow path for combustion gases includes a plurality of heat exchange tubes in semicircular array spaced from and generally coaxial with the furnace tube of the boiler.

A first tube sheet 20 is secu-red at a flanged joint 21 to end cap 14 by b'olts or welding or other suit-able means. Tube sheet 20 is also welded or otherwise secured to one end of shell 13. A second end cap 22 is secu-red t-o plate 1S and the other end of shell 13 at fiange 23 by bolts or welding or other suitable means. End caps 14 and 22 are removable at fianges 22 and 23, being secured by means of bolts or the like, so that the end caps 14 and 22 and plate can be removed for servicing of inter-nal parts and cleaning or replacement of boiler tubes when desired or needed.

A second tube sheet 24 provided opposing tube sheet and is suitably secured by weld-ing or the like to the inner wall of shell `13. Tubes 10 extend between and are secured through t-ube sheets 20 and 24 using usual tube sheet and tube mounting techniques. A water and/or steam chamber 25 is defined between tube sheets 2() and 24 and within shell 13; tubes 10 pass through chamber 25. Water supply or feed inlets 28 are provided in shell 13 for charging water to chamber 25 and a steam outlet 29 is provided for withdrawal of Isteam from chamber 25. Indicated at 30 are fittings through shell 13 for attachnient of pressure gauges or the like, which fittings may be plugged or capped when not used.

An oil burner 31 is provided mounted in refractory material 32 secured within a furnace tube 33. The semicircular array of tubes 10 extends over the top of furnace 33 and laterally downward on each side thereof. Tubes 10 are each spaced from furnace 33.

Burner 31 includes a nozzle for discharge of fuel, eg. in the form of oil or oil-air mixture, and stationary impellers 35 adjacent the nozzle for direction of an air supply for admixture with fuel ejected from nozzle 34. Nozzle 34 is supplied with fuel through oil feed line 3S and the burner 31 is supplied with air by fan 39 driven by motor which draws air from air inlet 41 and forces the air through lair chamber 42 against impeller blades 35. Adjacent the nozzle 34, a circumferential thick layer of fire resistant insulation is provided on the interior face of furnace 33. Furnace 33 is supported by tube sheets 20 and 24 adjacent opposing ends of the furnace 33, the furnace passing through a large circular aperture in each tube sheet and being welded or otherwise suitably secured to the tube sheet. Burner 31 is supported by suitable mounting means from end plate 15 andis removable therefrom for servicing.

Tracing now the flow of materials thro-ugh the boiler, oil or other suitable fuel is burned at nozzle 34 which is supplied with air from inlet 41 and supplied with fuel through line 38 in the direction of the arrows shown. The combustion gases are formed in and flow along furnace 33, as shown by the arrows. Chamber 25 has been filled with water to the level desired through inlet 28 and the combustion gases passing down fire tube 33 heat the water within the boiler chamber by heat exchange. At the right-hand end of furnace 33, as viewed in FIGURE 1, the combustion gases are redirected from the outlet end 45 of furnace 33 into inlet ends orf the plurality of heat exchange tubes 110 forming an arched or curved array around at least the upper portion of furnace 33. The combustion gases flow from the outlet ends of tubes 16 to outlet chamber or manifold 49 and thence to discharge.

Cap 14 includes a pressure release valve in the form of a pressure-loaded cover 50. Further cap 14 defines a chamber in conjunction with tube sheet 20 which serves as a conduit for directing return of combustion gases through the boiler chamber via tubes 10. As the oombustion gases pass lor return through tubes r10, further heat exchange with the surrounding water in chamber 25 is effected.

The operation of `the boiler is convention-al for a horizontal tube boiler employing a fire tube type furnace for generating hot water or steam or the like.

It will be noted that `furnace 33 is corrugated for increased surface area ffor heat exchange with the water in the boiler. In addition, the cross-sectional area 'and diameter of the furnace tube decrease along the length thereof as viewed in FIGURE 1 from left to right, the decrease in diameter in the illustrated form being in the form of steps. The stepped configuration not only compensates for the decrease in volume of combustion gases las they become cooler near end 45 than near 44 within furnace 33, but also is advantageous from the standpoint of permitting incline of tubes 10, e.g. to the right as viewed in FIGURE 1, in a prefer-red for-m of the present invention for drainage purposes as described above.

We claim:

1. A heat exchange tube assembly comprising a plurality of long tubular members each having an inlet end, an outlet end and a spiral array of bosses on the interior surface, said spiral array including a plurality of bosses for each spiral convolution off the spiral array, the remainder of the interior surface being substantially boss-l free and including a boss-free straight interior surface portion constituting a straight drain trough extending the length of the tubular member, each boss of said array being spaced angularly and axially from the next adjacent boss of said array, and tube sheet means mounting tubular members at each end thereof and disposing the tubular members at a slight incline from the horizontal with the drain trough surface disposed at the bottom of the tubular members for draining condensate from the tubular members.

2. The tube of claim 1 wherein each of said bosses is an oblong boss having its length disposed along the length of said member.

3. A heat exchange tube comprising a long tubular member having olpposing open ends and a generally Aarinular wall of relatively uniform cross-sectional area and diameter throughout its length, a plurality of indentations from the exterior of said wall defining dome-like spaced bosses in spiral array on the interior surface of said wall along at lea-st a portion of the length thereof, a boss-free longitudinal interior trough along the interior of said tube defined between pairs of adjacent bosses of said array, and means mounting said tube horizontally `and on a slight longitudinal incline in a position with said boss-free trough defining the lower internal surface of `said tube for drainage of condensate therefrom.

4. The heat exchange tube assembly of claim 1 whereineach convolution is defined by four said bosses spaced an angular distance of on center from each other and an axial distance from each other of approximately 0.4 diameter of said tubular member.

5. The heat exchange tube of claim 4 wherein each of said bosses is defined by an indentation of the tubular member wall from the outer surface thereof, said indentation having a radius R1 o-f approximately one-half the radius of said tubular member and wherein each boss merges laterally with the tubular member inner surface through a curved surface having a nadius approximately one-third 0f R1.

6. The heat exchange tube of claim 5 wherein the ratio of the depth of said indentation to the diameter of the tubular member is approximately 1:4.

7. A boiler comprising a shell defining an enclosure, heating means for providing hot fluid in heat exchange proximity with said enclosure, a pair of opposing facing tube sheets generally vertically mounted within said shell adjacent opposing ends of said enclosure and defining a chamber therebetween within said enclosure, an inlet and outlet through said shell for delivering feed to and delivering product from said chamber, a plurality of generally horizontally disposed heat exchange tubes mounted through said chamber in heat exchange therewith, each ot said tubes having opposing open ends communicating with said enclosure exteriorly of said chamber and beyond said tube sheets, and [means for directing hot combustion gases from said heating means to an inlet end ot each heat exchange tube, each heat exchange tube comprising a tubular member having an inner surface including a plurality ot bosses in spiral array defining a spiral brush cleaning path through the tube between the bosses, each convolution of said spiral array comprising a plurality 6 of spaced separate bosses, said bosses in each convolution ot said spiral arr-ay being aligned linearly relative to bosses in the remaining convolutions defining a straight `brush cleaning ,path through the tube between the bosses including an unbossed surface comprising a trough traversing eonvolutions ot the spiral array and extending `from one end of the tube to the other, said tubes being disposed and mounted by said tube sheets inclined lengthwise slightly from horizontal from one end tio the other with said unbiossed trough surface disposed at the bottom oit each tube for gravity dnainage of condensate across the spiral path detined by said bosses and from the tube.

References Cited by the Examiner UNITED STATES PATENTS 1,922,838 8/1933 Bossart 165-177 2,189,135 2/ 1940 Dickson 122-149 2,252,645 8/1941 Spanner 165-177 2,343,542 3/1944 Faunce 165-133 2,604,081 7/ 1952 Hene 122-149 FOREIGN PATENTS 679,285 8/1939 Germany.

ROBERT A. OLEARY, Primary Examiner.

KENNETH W. SPRAGUE, CHARLES SUKALO,

Examiners. 

7. A BOILER COMPRISING A SHELL DEFINING AN ENCLOSURE, HEATING MEANS FOR PROVIDING HOT FLUID IN HEAT EXCHANGE PROXIMITY WITH SAID ENCLOSURE, A PAIR OF OPPOSING FACING TUBE SHEETS GENERALLY VERTICALLY MOUNTED WITHIN SAID SHELL ADJACENT OPPOSIING ENDS OF SAID ENCLOSURE AND DEFINING A CHAMBER THEREBETWEEN WITHIN SAID ENCLOSURE, AN INLET AND OUTLET THROUGH SAID SHELL FOR DELIVERING FEED TO AND DELIVERING PRODUCT FROM SAID CHAMBER, A PLURALITY OF GENERALLY HORIZONTALLY DISPOSED HEAT EXCHANGE TUBES MOUNTED THROUGH SAID CHAMBER IN HEAT EXCHANGE THEREWITH, EACH OF SAID TUBES HAVING OPPOSING OPEN ENDS COMMUNICATING WITH SAID ENCLOSURE EXTERIORLY OF SAID CHAMBER AND BEYOND SAID TUBE SHEETS, AND MEANS FOR DIRECTING HOT COMBUSTION GASES FROM SAID HEATING MEANS TO AN INLET END OF EACH HEAT EXCHANGE TUBE, EACH HEAT EXCHANGE TUBE COMPRISING A TUBULAR MEMBER HAVING AN INNER SURFACE INCLUDING A PLURALITY OF BOSSES IN SPIRAL ARRAY DEFINING A SPIRAL BRUSH CLEANING PATH THROUGH THE TUBE BETWEEN THE BOSSES, EACH CONVOLUTION OF SAID SPIRAL ARRAY COMPRISING A PLURALITY OF SPACED SEPARATE BOSSES, SAID BOSSES IN EACH CONVOLUTION OF SAID SPIRAL ARRAY BEING ALIGNED LINEARLY RELATIVE TO BOSSES IN THE REMAINING CONVOLUTIONS DEFINING A STRAIGHT BRUSH CLEANING PATH THROUGH THE TUBE BETWEEN THE BOSSES INCLUDING AN UNBOSSED SURFACE COMPRISING A TROUGH TRAVERSING CONVOLUTIONS OF THE SPIRAL ARRAY AND EXTENDING FROM ONE END OF THE TUBE TO THE OTHER, SAID TUBES BEING DISPOSED AND MOUNTED BY SAID TUBE SHEETS INCLINED LENGTHWISE SLIGHTLY FROM HORIZONTAL FROM ONE END TO THE OTHER WITH SAID UNBOSSED TROUGH SURFACE DISPOSED AT THE BOTTOM OF EACH TUBE FOR GRAVITY DRAINAGE OF CONDENSATE ACROSS THE SPIRAL PATH DEFINED BY SAID BOSES AND FROM THE TUBE. 